Rotary thumbwheel voltage divider switch



Jan. 24, 1967 H. GABRIELIAN ROTARY THUMBWHEEL VOLTAGE DIVIDER SWITCH Filed March 4, 1964 2 Sheets-Sheet 1 FIG. 1.

HENRY GABRIELIAN AGENT Jan 24, 1957 H. GABRIELIAN ROTARY THUMBWHEEL VOLTAGE DIVIDER SWITCH 2 Sheets-Sheet 2 Filed March 4, 1964 FIG. 5.

INVENTOR. HENRY GABRIELIAN BY mm AGENT United States Patent O M 3,300,748 RGTARY THUMBWHEEL VOLTAGE DIVIDER SWlTCI-I Henry Gabrielian, Santa Ana, Calif., assigner to Electronic Engineering Co. of California, Santa Ana, Calif.,

a corporation of California Filed Mar. 4, 1964, Ser. No. 349,319 10 Claims. (Cl. SSS- 200) My invention relates to switched adjustable voltage dividers and more particularly to a novel type of voltage divider assembled upon the structure of a thumbwheel rotary switch.

Certain voltage divider circuits having desirable properties, such as the Wolff-Poggendorf voltage divider, have heretofore been adjusted in voltage output by employing a plurality of relays. With the WoliT-Poggendorf voltage divider each such relay was provided with contacts and connected so as to short one resistor ofthe voltage divider at the same time as a correspondingly valued resistor was unshorted in the opposite part of the device. This provides a constant-current mode of operation.

A significant simplification is achieved by the subject invention wherein a switch struct-ure itself provides the necessary Wolff-Poggend-orf switching mode and relays are not required.

Additionally, by mounting the resistors involved upon the mechanical switch structure, highly desirable short connecting leads are employed and freedom from crosstalk and interference is secured.

y The saving in space, weight and cost over the rel-ay ernbodiment lof the prior art is obvious. These advantages become particularly important when multiple units of the voltage divider are considered, such as a three gang unit providing 0.1 volt steps from to 99.9 volts.

A preferred embodiment of my inventi-on employs a thumbwheel type switch having a plurality of stationary contacts arranged in concentric tracks, each with one rotary wiper Contact. An additional, preferably outer track is also provided, having two circumferentially spaced wipers. The additional track is arranged to provide contact between a stationary contact and one Wiper at any given time and with the other wiper at another given time, in which way I obtain the function of two tracks in a single track. Two groups of series-connected` resistors are preferably mounted on the same card or board which carries the stationary contacts and are connected to these contacts such that when lone resistor in one group is shorted by the rotation of the thumbwheel to a given position a resistor of corresponding resistance value is unshonted in the other group. This provides a constant current circuit. The output is taken across one group of resistors. The resistance ratio is altered thereacross for each position of the thumbwheel and when an energizing source of voltage is provided the voltage at the output is altered in an equivalent manner, thus providing the adjust- .able voltage divider.

An object of my invention is to provide a switched constant current voltage divider.

Another object is to provide a switched voltage divider having fewer switching tracks than is ordinarily required.

Another object is to lprovide a compact swit-ched voltage divider.

Another object is to provide a Wolfi-Poggendorf voltage divider devoid of relays.

Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawings, in which are set forth by way of illustnation and example certain embodiments of my invention.

FIG. 1 shows a simplified schematic circuit of a single section Woll-Poggendorf voltage divider,

Patented Jan. 24, 1967- gce FIG. 2 shows a three-section embodiment of the same, FIG. 3 shows the contact side of'a switch board with the locations of the resistors indicated, and FIG. 4 shows a rotor with wipers and the accompanying thumbwheel.

In FIG. 1 the first group of resistors is identified by numerals 1, 2, 4, 2;.these numerals also suggesting the relative resistance values required. That is, for a low impedance voltage divider the value of resistor 1 may be 10 ohms, of 2 20 ohms, of 4 40 ohms, and of 2 20 ohms.

For a high impedance divider these may be 10,000 ohms,

. examples given.

The second group of resistors is identified by numerals T. These have corresponding resistance values and are located opposite in the circuit having they same designatio-n in the iirst group. Th-atis, when resistor 1 is shorted out of circuit, resistor is unshorted and placed in circuit; the-same with resistors Zand and so on.

The input to the voltage divider 4is provided at E1, as by a battery 10 or an equivalent regulated power supply. The output is taken from across all `of the second group of resistors; i.e., lat E0.

The manner in which |the voltage ydivider is adjusted is indicated generally by the arrow contacts and the adjacent shor-ting bars in FIG. 2. The adjustment will first be recited with respect to FIG. 1. When the thumbwheel switch is positioned at the 0 (zero) index thereof, resistors 1, 2, 4, 2 and 1 are in circuit and resistors E, T are shorted. This, of course, makes the vol-tage Eo=0. With the thumbwheel in position 1, resistors 2', 4, 2, 1" and are in circuit and resistors T and 1 are shorted. This inserts a resistor having a resistance value of 1 in the Eo shunt path and removes one of the same value from the iirst group of resistors. This gives a voltage output corresponding to unity and also keeps the current flowing in the complete series `circuit constant, as is indicated by the constant I legend in FIG. 1.

With the thumbwheel switch in position 2, resistors 1, 2, 4, 1 are in circuit and resistors are shorted. This inserts resistor having a resistance value of 2 in the E,J shunt path and removes'one of the same value from the first group of resistors. This gives a voltage output corresponding to two and again keeps the current owing inthe complete series circuit constant. By unshorting one or more resistors at any one time in the group of resistors it is seen that Ia total resistance urp to the value 9 in'that arm may be yplaced in circuit. Thus, voltage values from zero to nine are caused to appear in the output circuit E0, and the output voltage is adjustable j over this range in. unit increments.

Frequently it is desired that the adjustment of the voltage divider be over a greater range or with finer steps, or both, and this is obtained by duplicating the structure of FIG. 1 plural times with resistor values ten times 'greater in each decade from the smallest increment of adjustment to the largest.

Such -a structure is shown in FIG. 2. The source of voltage 10 is as before, although this may have a larger value, :as volts. Variable -resistor 11 is placed in series' with source 10 to provide a ne adjustment of the voltage of that source to, say, exactly 100 volts. Across terminals 12 and 13, then, appears the input voltage El.

At the rst decade to the left of terminal 12, the tens decade, resist-ors 1t, 2t, 4t, 2t' in the rst group are con-- nected in series; and to the left of terminal 13 resistors t, t, it, t in the second group rare connected in series.

These have the same relative resistance values as was set forth in considering FIG. 1; in this case 10,000 ohms for 1t, 20,000 ohms for 2 etc.

Each of the eight resistors involved in this decade are connected to individual stationary contacts upon the card of the thumbwheel switch structure, as is shown in FIG. 3. I-n FIG. 2 these are contacts 14 and 15 as related to resistor 1t. A shorting wiper 16 is disposed upon the rotor thumbwheel of the switch and is in an operative relative to contacts 14 and 15. A corresponding pair of contacts 17 and 18 connect to resistor and a shorting wiper (a movable contact) 19 is in an operative relation to these contacts.' As will be later disclosed, the operation of the thumbwheel switch is such that when contacts 14 and are not shorted by wiper 16 contacts 17 and 18 are shorted by wiper 19, and vice versa. Element 20 is schematic for an insulating actuating member that moves both wipers 16 and 19 together and dotted line 21 is schematic for the thumbwheel rotor, indicating that all wipe-rs move together. k

In the tens decade in FIG'. 2 it will be noted that resistor is not shorted, for purposes lof illustration. This contributes 4to the output voltage the voltage drop iacross 40,000 ohms, which is equivalent to 40 volts in the voltage divider of FIG. 2.

Through interconnecting terminals 22 and 23 a second decade, the units decade, is connected to the whole electrical structure of the ganged voltage divider of FIG. 2. The connection of the resistors, their relative resistance values, arrangement for shorting and unshorting, land so on are the same as for the tens decade just described. The resistors are given the subscript u to designate that they are a part of the units decade. These resistors have absolute vialues 1A() that of the tens decade.

In the units decade wiper 25 shorts resistor` 2u in the illustrative condition shown. Resistors 2u, 4u are not shorted. The values of these resistors are 1,000, 2,000, 4,000 ohms, respectively. The contribution of this series is thus 7,000 ohms. This is equivalent to 7 volts in the voltage divider of FIG. 2. In this units decade, resistors 1u, 2u, 4u are shorted by wipers 26, 27, 2S, respectively, in order that the constant current aspect of the voltage divider be maintained.

In Ia similar manner, and through interconnecting terminals and 31, connection is made to the tenths decade from the units decade. As before, the connection of the resistors,V the relative resistance values of each, the arrangement for shorting, and so on are the same for the decades previously described. These resistors are given the subscript s to designate that they are a part of the tenths decade. They have absolute values 1/10 that of the units decade.

In the tenths decade as shown, resistor I, is not shorted, While the others in the second group fare shorted. This provides a voltage drop across 100 ohms, which is equivalent t-o 0.1 volt in the voltage divider of FIG. 2. In the tenths decade, resistors 2 5, 4s, 2S are shorted by wipers 32, 33, 34, respectively, in order that the constant current aspect of the voltage divider be maintained.

Since the tenths decade is the last in this embodiment, la resistor 1s is connected between terminals 36, 37, which also connect to the beginning of the first :and second groups of resistors; i.e., resistor 1s and resistor '17s. The value of resistor 1s in this embodiment is 100 ohms.

In FIG. 2 the feedback voltage E0, that is, the adjustable voltage providing ,the desired output, appears between terminals 13 and 37. With the wipers in the positions shown in the gure themagnitude of this voltage is 47.1 volts. In order to preserve accuracy of they voltage divider function the circuit connected across terminals 13 and 37 should have a very high impedance, such as the input to a digital voltmeter, vacuum tube voltmeter, ror the dellection plates of an oscilloscope. A specific appli-cation for my device is the use with an lanalog voltage comparator tor go/ no go testing.

FIG. 3 lshows the rotor contact side ofthe switch board or card, with the resistors for one decade, as in FIG. 1, indicated schematically and connected to the circuit wiring upon the board. Other circuit wiring is also required. This is norm-ally positioned on the reverse side of the board. In FIG. 3 this other circuit wiring is shown dotted. Thus, the complete electrical circuit fora voltage divider vdecade is shown in one gu-re, with the significant contacts and circuit coacting with the rotor Wipers set forth according to the geometry of an actual embodiment. In this way all of the details of the invention is most easily comprehended. v

The board 40 upon which etched or printed circuits may be formed is of usual material for this purpose, such as epoxy-filled fiberglass. While size is not definitive of invention herein, the board may be 3% long by 1% wide by 1/16 thick. Aperture 41 is provided as a bearing for a short shatt attached to the rotor, which rotor carries the wiper contacts. Surrounding the aperture are tive concentric tracks of stationary contacts. These are identied by designations T1 through T5. As will be noted more particularly in FIG. 4, the wipers are disposed at differing radial distances, one to intercept the stationary contacts of one track. The several individual stationary contacts, such as 42, 43, 44, 45 in FIG. 3, -are disposed to accomplish the shorting and unshorting routine set forth in the discussion of FIGS. 1 and 2.

Bach small circle upon these contacts represents a connection hole trom one side of the boa-rd to the other. Each hole either accommodates a soldered connection betweene printed circuit conductors on one side to the other, or, in the case of resistors required for the voltage dividing function, the soldered connection of the resistor pigtails to the conductors of the circuit board. Circle 46 is illustnative of the first use and circle 47 of the second use.

Several printed circuit conductors extend from the circumferential contacts to the resistors of the voltage divider. For example, from the extended contact at track T1 conducto-r 48 connects to the left-hand side of resistor and continues onward, downward, and then to the right to form terminal 49. The several aligned terminals 50, 51, etc. are lat an extending tab 52 of board 40 and are arranged to engageg contacts in an elongated female socket, such as is known for making connections to external circuits in this technique. Similarly, from stationary switch contact 42 conductor 53 connects to the righthand end of resistor 4.

It will be noted that the stationary contacts 42, 43, 44, 45, etc. have dilterent sizes and shapes. This provides contact therewith by a given wiper for more than one switch position; which, in the case of the ten position switch illustrated, is 36 from one switch position to the next. Als-o, certain contacts extend to more than one track. As an example, the contact T4 is largely resident in track 4, but it yals-o has a small upper extension to the right into the inner track 5.

The several resistors shown in FIG. l; i.e., 1, 2, 4, 2', b2", '27, are also shown rat the right side of card 40 in FIG. 3; with top :and bottom connections on the card shown in full and dotted lines, respectively. Illustrative resistance values for these resistors have been given in connection with FIG. 2. Resistor 1 is also shown.

The rotor, the wiper contacts and the thumbwheel are shown as a unit in FIG. 4. This assembly is shown to the same scale as employed for the board of FIG. 3. Shaft 60 fits into aperture 41 of board 40. This results in the showing of FIG. 4 being inverted planarly. Thus, wipers 61, 62, 63, `64, 65, 66 bear upon tracks T1 through T5 upon the board.

It will be noted from FIG. 4 that the pairs of wipers 61, 62; 63, y64; and 65, 66 yare spaced apart 120 circumferentially. Wipers 61 and 63 both bear upon outer track T1 of FIG. 3, The stationary contacts thereof, of which 42 and 44 are examples, are so formed that when Wiper 61 is contacting a station-ary contact wiper 63 is not so contacting, and vice versa. In this way a hidden track is provided, which results in live tracks functioning as six tracks. This reduces the diameter of my device and result in other understandable economies.

The wipers per se lare formed of circular contact wire, such as the known Paliney #7 material, and may be approximately 1&4 inch in diameter by 3A6 long. These Wipers are spot-welded to berylliumvcopper or equivalent spring plates 67, 68 and 69 in pairs as shown. Each plate is provided with live lingers, as lingers 70 for plate 67. This allows a wiper t-o be attached to a linger to track upon any of the five tracks T1 through T5, as has been set forth. On plate 67 the lingers 70 corresponding to tracks 1 (outer) and 5(inner) are provided with wipers 61 and 62. Since there is continuous metallic connection between these two wipers through plate 67, it is seen that contact between these wipers and stationary contacts of the tracks will result in a connection from one track to the other. When the lingers are -to |be used to support wipers the lingers are bent upward from the otherwise planar disposition of the plate, so that contact will be made only by bend near the free end of the wiper to the stationary contacts. The wipers are each given a slight bend at near the free end thereof so `that the contact formed is suited for rotation of the rotor in either direction. This bend is indicated in FIG. 4 by shading upon each of the wipers.

On plate 68 the lingers 7 0 corresponding to tracks 1 and 2 are bent up yand support wipers 63 and 64. On plate 69 the lingers 70 corresponding to tracks 3 and 4 are bent up and support wipers 65 and 66.

Each of the plates 67, 68 and 69 are fastened to an insulating rotor disk 71 by two eyelets 72. The rotor may be formed of a :material such as epoxy-filled liberglass. The rotor, in turn, is fastened in a thumbwheel housing 73 and correctly circumferentially positioned therein by intruding molded key 74. The thumbwheel has a plurality of projections 75, normally ten, and upon a flat surface adjacent to each projection there is engraved a numeral; the one adjacent to key 74 being the numeral 5. For a decade switch the numerals run from 0 through 9, counterclockwise in FIG. 4.

On the obverse side of the thumbwheel of FIG. 4 for a decade switch a ten 4hole and spring ridge circumferential detent may be positioned. This coacts with two plastic balls seat-ed in depressions in a stationary switch housing that surrounds the thumbwheel. Since these elements are known and do not enter inventively into the structure being described they have not been illustrated. The thumbwheel 'may be -molded of any suitable material, of which the phenolics are representative. Typically, the material used is colored black, or some other color for coding in the equipment in which the thumbwheels are used, with white lor black lilled numerals to indicate the position of the decimal thumbwheel.

While the use of printed circuits (and/or etched circuits) has been mentioned in the description of the preferred embodiment, it will be understood that hand-wired connections and inserted metallic stati-onary contacts may also be employed. The form and function of these alternate elements is essentially the same as those shown. Also, the use of known commercial resistors having pigtail conductors for connection at each end has been inferred in the description herein above. Alternately, the resistance required may be obtained by depositing metal lilms upon board 40 at appropriate places, -as by vacuum deposition. For -such yan arrangement the conliguration of the connecting conductors, such as 48 and 53, may be altered to give a longer path for a high resistance resistor and vice-versa.

In the multiple decades embodiment of FIG. 2, in which another decade is connected to the output of a given decade, the effective resistance of the following decade equals the resistance of the otherwise terminating resistor 1, thus such a resistor is not used. Note the absence thereof between terminals 22 and 23, and between terminals 30 and 31 in FIG. 2.

Still other modifications may be made in the characterv istics of the circuit elements, details of circuit connections,

and the arrangement size, proportions and shape of elements inthe illustrative embodiment shown Without departing from the scope of my invention.

Having thus fully described my invention and the manner in which it is to be practiced, I claim:

1. An ladjustable voltage divider comprising (a) a multiposition thumbwheel rotary switch having plural stationary contact tracks with each of said tracks having one rotary wiper and (b) an additional track having plural stationary contacts, and two circumferentially spaced rotary wipers,

(c) a lirst group of series connected resistors which are connected to a first group of said stationary contacts, and

(d) a sec-ond group of series connected resistors which are connected to a second group of said stationary contacts and in series with said lrst group of resistors,

(e) imeans to rotate all of said rotary wipers in common,

(f) whereby, upon a resistor of said lirst group being shorted by a first wiper coactive with said lirst group of stationary contacts a resistor of said second group is unshorted by a second wiper at a dillerent circumferential position than that of said lirst wiper, said second wiper coactive with said second group of stationary cont-acts, t-o alter an output voltage obtainable from said voltage divider by altering the resistance ratio between opposite ends of said lirst and second groups of series connected resistors.

2. The voltage divider of claim 1 in which (a) Ian equivalent of a second said Iadditional track is obtained by providing a spacing of approximately between two circumferentially spaced rotary wipers, and

(b) providing stationary cont-acts on said additional track to contact only one of said two wipers at one given circumferential position, and only the other of said two wipers at another given circumferential position.

3. The voltage divider of claim 1 in which (a) said one wiper for one said plural stationary track is disposed at la dilierent position circumferentially than said one wiper for another one of said plural stationary tracks.

4. The voltage divider of claim 1 in which (a) one of said one wipers is circumferentially disposed at the same position as one `of said two circumferentially spaced rotary wipers, and

(b) two of said one wipers are located in common at .another circumferential position.

5. The voltage divider of claim 4 in which (a) each of said wipers that is circumferentially disposed at the same location as another wiper is electrically connected thereto.

6. The voltage divider of claim 1, which additionally includes,

(a) an insulating card, and

(b) said plural stationary contacts and electrical connections therefrom to said first and -said second groups o-f resistors are affixed to said card.

7. The voltage divider of claim 1 in which (a) the resistance of individual resistors in said lirst group of series connected resistors have the ratio one, two, four, two; and

(b) the resistance of individual resistors in said second group of series connected resistors have the ratio one, two, four, two and are connected in the same order to said second group of stationary contacts as are the said rst group `of said series connected resistors connected to said first group of station-ary contacts.

8. The voltage divider of claim 1 in which (a) `an additional resistor is connected between one end of said first group of series connected resistors and the corresponding end of -said second group of series connected resistors.

9. A multiple adjustable voltage divider according to claim 1 having y (a) a plurality of said thumbwheel switches,

(b) means to conect all of said plurality of said iirst group of series connected .resistors in series,

(c) means toconnect all of said plurality of said second group of series connected resistors in series, and

(d) means to provide the adjustable voltage across all of said plurality of said second group of series c-onnected resistors.

16. The multiple adjustable voltage divider of claim 9 in which (-a) the resistance of said first group of series connected resistors in one said plurality is a multiple of the resistance of said rst group of series connected resistors in another of said plurality, and

(b) the resistance of said second group of series connected resistors in said one plurality is the same multiple of the resistance of said second `group of series connected resistors in the same other of said plurality.

References Cited by the Examiner UNITED STATES PATENTS 2,511,924 6/1950 Lee 338--200 2,853,564 9/1958 Gahagan. 2,896,033 7/1959 Hartz. 3,152,288 10/1964 Broadhead.

RICHARD M. WOOD, Primary Examiner.

J. G. SMITH, Assistant Exdminer. 

1. AN ADJUSTABLE VOLTAGE DIVIDER COMPRISING (A) A MULTIPOSITION THUMBWHEEL ROTARY SWITCH HAVING PLURAL STATIONARY CONTACT TRACKS WITH EACH OF SAID TRACKS HAVING ONE ROTARY WIPER AND (B) AN ADDITIONAL TRACK HAVING PLURAL STATIONARY CONTACTS, AND TWO CIRCUMFERENTIALLY SPACED ROTARY WIPERS, (C) A FIRST GROUP OF SERIES CONNECTED RESISTORS WHICH ARE CONNECTED TO A FIRST GROUP OF SAID STATIONARY CONTACTS, AND (D) A SECOND GROUP OF SERIES CONNECTED RESISTORS WHICH ARE CONNECTED TO A SECOND GROUP OF SAID STATIONARY CONTACTS AND IN SERIES WITH SAID FIRST GROUP OF RESISTORS, (E) MEANS TO ROTATE ALL OF SAID ROTARY WIPERS IN COMMON, 